High frequency oscillator



y 1935. c. w. HANSELL HIGH FREQUENCY OSCILLATOR Filed July 28, 1950 L L m Y RM M O R MW 0 E H mm .A M M C Y B J Y i J W m I w Patented May 14, 19 35 PATENT OFFICE men FREQUENCY osomm-roa Clarence W. Hansel], Port Jeflerson, N. Y., as-

signor to Radio Corporation of America, a cor-' poration of Delaware Application July 2a, 1920, Serial No. 471,309

1 Claims. (01. ass-cs) This invention relates to high frequency generators and more particularly to the type of high frequency generator which can produce waves of ultra-high radio frequency.

Heretofore the production of high frequency A pensive apparatus, and other respects, compared to the transmission by long waves. While the generation of high frequency oscillations of the order of 60,000 kilocycles or less has been found possible heretofore, the production of higher frequencies with useful amounts of power has been very dimcult and has not been accomplished with the desired emciency.

The object of the invention is to produce high frequencies of the order of 300,000 kilocycles or more. Another object of the invention is to produce such frequencies by means of apparatus already developed for operation at lower frequencies. 'Another object is to produce such waveswith great facility and at small cost. Further objects will appear during the description oi the invention.

The'invention is more fully set forth in com bination with the accompanying drawing, in X which Fig. 1 represents schematically a longitudinal cross section of a device used to generate short radiowaves in accordance with my invention;

Rig. 2 is a transverse cross section through a tube known as the magnetron, which may also be used to generate these short waves; and

Fig. 3 represents an enlarged schematic view of the tube shown in Fig. 2.

In Fig.1 there is shown a device I comprising a filament 2 which. is energized by a source II of current which is shown as alternating, although direct current is equally applicable. At one end of the device is a flared oi" circular portion 4 so positioned that the filament is at, one end of a tangent portion 6 of the tube. 1 desig nates an opening in the circular portion of the in the customary manner. These electrons are attracted by the positively charged plate and travel in a substantially straight line along the portion 8 of the tube. The circular shell 0 may be given a charge similar to that of the filament, or may be made slightly more negative than the filament by battery H, in order to repel the electronic stream. The negative charge on the circular portion 0 will repel the electrons and cause them to bend around in themanner shown by the arrows in the figure. The opening I will be so positioned as to be in line with the electrons after they have followed the periphery of the curved portion 4.

when the electrons initially enter the shell 0 from the straight portion 6 they will have under proper conditions such a high velocity that they will fly past the anode 0 due to their own momentum. After curving, the electronic stream will point toward the anode, but before finally reaching the anode the electronic stream must cross its own path. In doing so it will interrupt the stream entering the curved shell 0 from the straight portion 0, due to the mutual repulsion between electrons. The oncoming stream from the filament will remain interrupted until the first electrons have reached the anode. The stream from the filament will then be enabled to pass by and enter the curved shell 0, and the process will be repeated periodically.

It will be obvious that the principle of operation of this device is quite similar to that of the ordinary air or steam whistle, and a comparison between the two will be an aid to un derstandlng this invention.

The frequency of interruption of the electronic stream will determine the frequency of the desired oscillation in the plate circuit. My experiments so far indicate that the frequency is dependent substantially on the anode voltage and increases with increase in voltage. In other words it is determined by the time taken for an electron to travel twice around the loop, which is determined by the anode voltage and the dimensions of the tube; that is, the time of onehalf cycle is equal to the time taken for an electron to traverse the shell 0.

Fig. 2 shows a cross section 01' a modification of the device in a more practical form. In this system, anordinary magnetron tube is used to obtain the desired high frequency oscillations. The customary cylindrical anode is shown at 22, and at the longitudinal axis of the cylinder is the filament 2,3. On the outside of the tube 7 will be attracted toward the anode 22 and these tend to .travel directly toward the anode.- An electron in motion constitutes an electric current and is subject to the same laws as a current-carrying conductor. The electrons moving across the magnetic field will have a force exerted on them at right angles to their 1 direction of motion and proportional to their velocity and to the strength of the magnetic field. The electrons will thus be forced to follow a curved path, as shown in Fig. 3, and if the field is of sufiicient strength, will not reach the anode at all but will return to the filament, following the image of theiroutward path, and giving up their kinetic energy in doing so. This is the-condition commonly known as cut off in a magnetron tube. At a critical plate voltage for a definite field strength the electronic stream will just skim the surface of the anode 22 and some of the electrons will strike the anode while others will return bya similarly shaped path to the filament. The complete path of the electronic stream from filament to plate and back to filament will be approximately that of a cardioid, as is shown in Fig. 3. If the plate voltage is increased all of the electrons will be attracted to the plate, and if the filament, will decrease. This will again allow. the flow of electrons from the filament toward the plate, and the process will be repeated periodically. The frequency will depend chiefly on the anode voltage and increases when the voltage is increased. In other words, it is determined by the time taken for an electron to travel from filament back to the filament and approximately equal to twice the length of time of such travel for a complete period. The strength of the magnetic field determines the amplitude of the oscillations and the efficiency but has relatively little to do with the frequency.

The wave form of the electronic current which fiows to the anode will ordinarily be quite far from a sine wave and will be more nearly rectangular in shape. Such a wave form is rich in harmonics and the useful output from the tube may be obtained at harmonics of the fundamental frequency by tuning the circuitsconnected between filament and anode to the harmonics.

. electrons at an angle into itself periodically.

he is not bound by this explanation of its operation. Experiments so far have produced oscillations having a wave length of centimeters, and it is easily possible to obtain wave lengths of 10 centimeters or less.

The structure set forth is merely illustrative and does not comprise the only means for obtaining these results; for example, the shape of the tube shown in Fig. 1 may be varied and the relative position of the electrodes changed. For

example, the filament may have other forms and shapes than those shown and may also be of the indirectly-heated type. The same is true of the other'elements. ofthe invention. Also, the ordinary three-electrode tube may be employed as a high frequency oscillator. In suchv a case the grid and the filament could be electrically connected so that both serveas the source of electrons, or the grid could be so biased as to emit secondary electrons which serve as the source of the high frequencies. It is obvious that water cooling of the anode and better vacuum will result :in greater efficiency and perhaps higher frequencies.

Having described my invention, what I desire to secure by Letters Patent of the United States is:

1. A device for producing ultra-high frequency oscillations, comprising a filament for emitting electrons, an anode for attracting electrons, and means for causing the stream of electrons to travel in a curved path so as to cross itself, said means comprising a curved shell which has a potential at least as negative as that'of the filament, the v anode being positioned in an opening in the curved shell and insulated therefrom.

2. A device for producing utra-high frequency oscillations, comprisingv a curved shell, a straight tube attached tangentially. to the curved shell, a filament in one end of the straight tube, an open-. ing in the curved shell near the point of attachment of the tube to the shell, and an anode positioned in said opening, the anode serving to attract the electrons from the filament and to accelerate them to such a velocity that they pass the anode. due to their momentum, traverse the curved path in the shell, and finallyreach the anode over a path which crosses upon itself.

3. In high frequency apparatus comprisingan electron emitting element and an anode, the meth- 0d of producing high frequency oscillations which comprises uni-directionally propelling along a straight line a stream of electrons in the form of a beam from said electron emitting element towards said anode, and deflecting .said stream of v 4. In high frequency apparatus comprising an electron emitting element and an anode, the method of producing high frequency oscillations which comprises uni-directionally propelling a stream of electrons in the form of a beam from said electron emitting element towards said anode along the shortest possible path therebetween, deflecting said stream of electrons into a curved path so that they stream crosses itself at an angle, thereby interrupting the incoming stream, and thereafter periodically interrupting the stream flow to produce oscillations of the desired frequency.

5. The method of producing high frequency oscillations which comprises constantly propelling a stream of electrons in a single direction along a confined path, and in said stream of electrons cross upon its own path at an angle periodically.

6. An oscillation generator device for producing ultra high frequency oscillations a,

stream, said anode belng positioned to e eivef filament for emitting electrons, an anode, means for maintaining said anode at a positive potential for attracting electrons, an element arranged to be in the path og the electrons on the side of said anode away from said fllament, means for maintaining said element at a negative potential with respect to said anode for deflecting said stream of v electrons into its own path at an angle after they have passed said anode for interrupting said said deflected electrons after they have their original path of travel. 1

7. The method of producing high frequency oscillations which comprises propelling a streamof electrons in a single direction along a confined path, and making said stream or electrons cross upon its own path atan angle periodically.

. CLARENCE W. HANSELL. 

